Many devices require for their operation exact milligram and submilligram amounts of mercury. An example of a device which uses small quantities of mercury is the arc discharge lamp. Virtually all of these lamps employ mercury as one of the vaporizable components. In current commercial lamps such as fluorescent lamps, it is common practice to mechanically dispense a drop of natural mercury into the lamp. This practice of mechanically dispensing mercury or other material works well because natural mercury is a fairly inexpensive commodity costing about $0.30/gram. A mercury droplet can also be contained within a small capsule which is placed in the lamp and opened after a lamp is sealed. See U.S. Pat. No. 3,913,999.
Recently it has been determined that the efficiency of certain lamps, i.e., low pressure mercury-rare gas discharge lamps, can be enhanced if the isotopic mixture of the mercury is changed from that which occurs naturally. See, for example, Electric Discharge Lamps, MIT Press, 1971, by J. Waymouth for basic principles of low pressure mercury rare gas discharge lamps and U.S. Pat. No. 4,379,252. The latter patent teaches efficiency gains in fluorescent lamps when the .sup.196 Hg isotope is increased from its natural occurrence of about 0.14% to about 3%.
Enriched isotopes of mercury are very expensive. For example, at current prices, mercury which has been enhanced to contain 35% of the .sup.196 Hg isotope costs about $500/milligram (mg). Accordingly, it can be seen that use of this material requires very strict controls on the amount employed. Further, such materials need only be used in submilligram or milligram amounts.
It is very difficult to weigh out milligram and submilligram amounts of mercury. A microscopic technique has been used in the past to obtain milligram and submilligram amounts of Hg. Different size grids corresponding to different masses of mercury are placed under a microscope. One obtains specific milligram and submilligram amounts of mercury by selecting a specific grid and placing a sufficient amount of mercury onto the grid to cover the grid, thus, obtaining the amount of Hg desired. This method is very time consuming and difficult due to the extreme difficulty of handling such minute amounts of mercury. This process is also very expensive due to the fact that accidents can easily occur resulting in a loss of mercury. Also, this method is dangerous to workers due to their exposure and handling of toxic mercury.